Yeah, it worked. It does go by combined vs. time, so the more human players, the less time it takes. I got the 50 hour challenge today. I used a hammer on the 100 hour challenge, though. That's just too much.
After I got the 50-hour reward song, I went to my factory stage for ten minutes and got six more songs, completing my collection. :P Now I'm working on stickers and trophies. I have 440 trophies or something. I got a ton of them in the coin launcher today.
EDIT: Here's something pretty interesting!
The Tanooki » 25 lost tracks discovered on SSBB disc